The innovation proposed here is a high performance, high fidelity simulation capability to enable accurate, fast and robust simulation of unsteady turbulent, reacting flows involving propellants of relevance to NASA (GOX/GH2, LOX/LH2 and LOX/LCH4). The key features of this proposed capability are: (a) Hybrid RANS-LES (HRLES) methodology, and (b) flamelet modeling for turbulent combustion, incorporated in a proven existing solver called Loci-STREAM which has been developed by the proposing personnel under funding from NASA over the last several years. Basic flamelet methodology has been incorporated in Loci-STREAM during Phase 1 work and tested on gas-gas injectors of relevance to NASA. The enhancements in Loci-STREAM resulting from Phase 1 work have demonstrated an order of magnitude improvement in simulation turnaround times relative to existing capability for turbulent reacting flow applications at NASA. The work proposed during Phase 2 will extend the flamelet methodology to real-fluid flows, wall heat transfer and variable pressures. This will ultimately result in a state-of-the-art design and analysis tool to enable the accurate modeling of for multiphase combustion in solid and liquid rocket engines, combustion stability analysis, etc. which constitute critical components of versatile space propulsion engines part of NASA's deep space missions.